1. Field of the Invention
A certain aspect of the present invention relates to an image scanning device and an image forming apparatus including the image scanning device.
2. Description of the Related Art
In a typical optical image scanning device, a document placed on a contact glass used as a document table is illuminated and light reflected from the document is detected by a CCD image sensor.
Normally, scanning parameters such as a linear scanning speed and a scanning distance are determined based on settings such as a document size, a resize ratio, and a scan density. Those settings are preferably performed automatically by the image scanning device rather than manually by the user (hereafter, “user” indicates all people who operate a device including an operator and a serviceperson) to improve user convenience and to prevent setting errors.
For example, patent document 1 discloses a method for automatically detecting a document size. In the disclosed method, the size in the main-scanning direction of a document is determined based on image data obtained by a CCD image sensor and the size in the sub-scanning direction is determined based on an output from a document detection sensor.
Patent document 2 also discloses a method for automatically detecting a document size where a scanning unit is placed in a position outside of an image scanning area while on standby, and is moved to a second position in the image scanning area to detect a document size when opening of a document pressing unit is detected.
Normally, a document detection sensor for detecting whether a document is present on a contact glass is used as a document size sensor for detecting a document size in the sub-scanning direction. If closing of a document pressing unit is detected when the document pressing unit is close to the contact glass, i.e., in the detection range of the document size sensor, the document size sensor may mistakenly detect the document pressing unit as a document even if no document is placed on the contact glass. To prevent this problem, in the disclosed method described above, an open/close detection unit is provided and configured to detect closing of the document pressing unit while the document pressing unit is at an angle with the contact glass that is large enough to prevent the document size sensor from mistakenly detecting the document pressing unit as a document. With this configuration, however, the light source is turned on while the document pressing unit is at a large angle and the light from the light source may enter the eyes of the user. Such light from the light source may damage the eyes of the user and at least causes the user to feel uncomfortable.
Thus, contrary to the above solution, the open/close detection unit must be configured to detect closing of the document pressing unit when the document pressing unit is at a low angle to prevent the light from entering the eyes of the user. Although the two conflicting problems may be solved by using a high-performance document detection sensor, this approach increases the production costs of an image scanning device.
Meanwhile, patent document 3 discloses an image scanning device where a light source is turned on as soon as an open/close sensor detects closing of a platen cover, but the intensity of light from the light source is set at a low level while the platen cover is being closed. This configuration, however, increases the costs of a lamp inverter.
[Patent document 1] Japanese Patent Application Publication No. 2006-254182
[Patent document 2] Japanese Patent Application Publication No. 11-196235
[Patent document 3] Japanese Patent Application Publication No. 2005-195785